[zippy5]

Hypothetically, it seems that your problem has to do surfaces being reflective in the visible light spectrum. Do you have any luck with ultrasonic, ultraviolet, or IR sensors?

Also I was also thinking about how light source estimation might be viable work around for reflective surfaces. http://www.thomaswhelan.ie/Whelan16ijrr.pdf

[cpgxiii]

Near-IR, which many of the available ToF (Kinect2, K4A, Basler/Lucid/Sony), active stereo (Realsense D4xx, Mynt, plenty more), and many some structured light (all Primesense derivatives, some older Realsense) cameras use, as well as close UV frequencies, suffers much the same issues as visible light. Farther wavelengths in shortwave IR start to have different/better properties, but the costs of cameras are just astronomical (~$20K/camera). Farther UV is also possible, but eventually we're dealing with frequencies that are actually harmful.

I do think there's a lot of open possibility in using more than the traditional visible spectrum. Using polarized sensors to remove reflections, or hyperspectral cameras to reduce noise that only appears in certain bands are good ideas. The problem is that we've got lots of cheap imagers that are really well built for visible spectra, and not a lot outside that. Small hyperspectral cameras for things like agricultural drones do exist, but they tend to work by combining multiple sensors (one for each band) which works fine for the ranges a drone operates at but not very useful at the close range indoor robots need.

Ultrasonic has a rather bad name in the field, a lot of people having used absolutely terrible robots with basically useless ultrasonic rangefinders early in their careers. In theory sound could be really useful, and there are some very nice (and very expensive) imaging sonars for underwater robotics use, but I'm not aware of any high-resolution ultrasonic sensors for land robots. One minor challenge with ultrasonic sensors in real products is ensuring that they are inaudible to people and pets - when they are almost-audible they are extremely annoying or even painful.

[hwillis]

> but I'm not aware of any high-resolution ultrasonic sensors for land robots.

Sound cameras are very cool- passive sonar, but they're audio frequency and not usually depth-sensing. There's a lot of room for improvement there, but its a relatively unknown area and definitely hasn't found its niche.

High resolution air sonar is necessarily fairly large, which makes it decidedly unsexy. It also puts a lot of strain on the potential for a low cost BOM when the pcb and chassis are ~>12" wide.

> One minor challenge with ultrasonic sensors in real products is ensuring that they are inaudible to people and pets - when they are almost-audible they are extremely annoying or even painful.

One thing that really surprised me when I got into it was that this isnt a trivial problem. Part of it is practical- the cheapest and most common sensors are around 60-80 kHz (mechanical size makes them easy to produce, with the drawback of a high-ish time constant).

Getting above the range of domestic animals isn't too hard or inconvenient, but it's surprising how extensively evolution has adapted for sound in bats. If you want to avoid harming them you need to keep above ~150 kHz, which gives you a fairly uncomfortably small bandwidth before you're into the highly-attenuating frequency ranges. Underwater it's a different story (biological structures have difficulty resonating at MHz+) but the frequencies that would give you sub-millimeter precision (350 kHz) are way more inconvenient than 40 or 60 kHz. You need totally different types of piezos and the range is sharply limited unless you're projecting volumes that would deafen at audio ranges.

Im still very optimistic about the role of sonar even as cheap lidar and depth cameras crowd the space, but its pretty difficult today to make a truly good sensor.